1. Technical Field
The present invention relates to a current measuring apparatus, a test apparatus, a current measuring method, and a test method. More particularly, the present invention relates to a current measuring apparatus that measures electric currents received by an electronic device, a test apparatus, a current measuring method, and a test method.
2. Related Art
Conventionally, as an example of a current measuring apparatus that measures electric currents received by an electronic device, an apparatus, which includes a large current measuring power supply circuit mainly used for measuring electric currents that the electronic device consumes during an operation and a small current measuring power supply circuit mainly used for measuring leakage currents during quiescence of the electronic device, has been disclosed as disclosed, for example, in Japanese Patent Application Publication No. 2001-41997 and Japanese Patent Application Publication No. 2004-347421.
As a device manufacturing process has been miniaturized recently, a high-density and high-speed electronic device has been manufactured. In this way, since more lots of elements are switched at higher speeds, a CMOS circuit particularly consumes large currents during an operation of the electronic device. Therefore, the capacity of a smoothing capacitor for stabilizing a power supply, which is provided between a terminal of an electronic device under test and a ground in Patent Documents 1 and 2 should be larger than ever before. Moreover, the number of gates mounted on the electronic device has been increased along with highly densifying the electronic device, so that leakage currents tend to increase even if the electronic device is in a stationary state.
On the other hand, as the device manufacturing process is miniaturized, widths of a gate and an insulated portion of wiring become narrower. For this reason, leakage currents caused by bad insulation becomes more minute, and thus a detection of the bad insulation becomes more difficult.
On the contrary, according to a quiescent current measuring power supply circuit in Patent Document 1, when a large noise occurs in a voltage source for a reference voltage, electric currents to be supplied to the electronic device are largely fluctuated and thus a measurement of a minute leakage current becomes difficult. Moreover, when the capacity of the smoothing capacitor is increased, electric currents to be supplied by a power supply circuit become large in accordance with a difference between an output voltage and a reference voltage. However, when the electric currents supplied by the power supply circuit become large in accordance with the difference between the output voltage and the reference voltage, large noise currents are supplied and measured in accordance with a noise voltage of the output voltage.